German Patent Publication No. 199 29 393 refers to a method for controlling a device for varying the valve timing of an internal combustion engine, especially a camshaft control device having an hydraulically releasable starting quantity locking device. In this context, the camshaft control device is designed as a hydraulic phasing device which has a first component that is rotatably fixed to the camshaft and a second component that is in driving connection to the crankshaft. In this context, in the case of a so-called impeller advance device, the component fixed to the crankshaft is connected in a force-transmitting manner to the component fixed to the camshaft via at least one hydraulic working chamber. The at least one hydraulic working chamber is subdivided by an adjusting element inside the device into a so-called
A pressure chamber and a so-called B pressure chamber. Each of these pressure chambers is connected to a controllable and/or regulatable hydraulic valve by way of a hydraulic line. The hydraulic valve, in turn, is connected to a control unit via a data line. Engine oil, for example, is used as the hydraulic fluid, which is put under pressure, during the operation of the internal combustion engine, using an oil pump, in such a way that the pressure chambers may have the oil pressure applied to them as a function of the hydraulic valves.
However, in order to obtain an oil pressure required for application to the pressure chambers, the internal combustion engine has to be operated at least at idling speed. Particularly at the start of an internal combustion engine, this is not yet sufficient for a camshaft control because the oil pressure is too low. During the start of the internal combustion engine, in order that the camshaft shall not take up an undefined position because of mechanical friction, the camshaft control device is mechanically locked for this reason in a locking position, for instance, using a retaining pin.
In this context, the retaining pin engages with a corresponding bore, as soon as the oil pressure falls below a certain value, such as during shutting off the internal combustion engine. When a minimum oil pressure is exceeded, the retaining pin is then released again from the bore. To prevent the pin from jamming, various methods of releasing it are available, such as that referred to in German Patent No. 199 29 393. In that document, the hydraulic valve is referred to as being controlled using several high frequency-timed intervals during a specified duration or using a predefinable number of intervals, in such a way that a rapid alternating pressure application on the A and B pressure chambers takes place, and consequently a jamming of the retaining pin is avoided.
During idling, the camshaft control device is operated in a reference position. In particular, in a two-step camshaft control device, the reference position is equivalent to the locking position. In steplessly controllable camshaft control devices, however, this reference position may deviate from the locking position. After a cold start of an internal combustion engine, the internal combustion engine is frequently operated at an increased idling speed. Therefore, the locking position is determined in such a way that an optimal camshaft setting is present for the start of the internal combustion engine.
In this context, it can, however, happen that a camshaft control device is locked again by mistake, during operation, for instance, because a currently required camshaft control corresponds to the locking position, and the retaining pin moves into the bore provided for locking, because of a non-stable oil pressure in this position. Additional problems may arise if the camshaft control device was not locked at the end of the preceding driving cycle, or it disengages from the locking position too early at a start.
Thus, during idling, the camshaft control device of an internal combustion engine (ICE) is operated in a reference position. In a two-step camshaft control device, the reference position is equivalent to a locking position. In steplessly controllable camshaft control devices, this reference position may deviate from the locking position. In this context, it may happen that a camshaft control device may lock itself again during the operation by mistake, the camshaft control device was not locked at the end of the previous driving cycle, or it releases itself too early from the locking position in response to a start.